At the present time, there are a number of publications, the constructional solutions of which are aimed at improvement of the accuracy and interference immunity of measuring equipment operating as part of phase-comparison radio-navigation systems. The progress in development of digital methods and constructional means substantially contributes to solution of the problems involved in simplification of the phase meter construction and improvement of phase meter quality characteristics.
The phase-comparison radio systems most commonly employ compensation phase meters hooked around an electromechanical system. However, the measuring accuracy and dependability of said phase meters are not sufficient and are determined by characteristics of such mechanical components as gearboxes, gears, and thoothed and worm gearings.
Serious complications occur in solving the problem of direct data input from the meter to the computer serving to process the navigational data. The use of extra mechanical converters for transforming the mechanical action into the digital code still further impairs the accuracy in measurement of such a navigational parameter as the phase difference.
Known in the art is a mobile receiving means of the Jorac type phase-comparison radio-navigation system manufactured by Seiscor, comprising receivers and an indicator unit, constituting a compensation tracking phase meter circuit incorporating a synchro-type phase shifter, a motor, a phase detector and a mechanical transmission. The radionavigation parameter values are injected into the computer through an analog-to-code converter. The foregoing receiving means permits measuring the phase shift of the radio system, the measuring accuracy being low because of the use of mechanical components.
There is also known a digital tracking phase meter (cf. USSR Inventor's Certificate No. 617747, filed on July 30, 1978), comprising two input shapers, the outputs of which are connected through two respective switches to inputs of an OR logic element; a count pulse generator connected to other inputs of said switches; and two dividing counters, one of these being a variable dividing factor counter connected to outputs of a reversible counter and OR logic element. The phase meter also comprises a switch set, a phase cycle integer reversible counter, a binary phase quantizer, an inverter and an equivalence unit, the inputs of which are connected to outputs of the binary phsse quantizer and reversible counter, and the output whereof is applied to a third input of the first switch, to the switch set and to a third input of the second switch through the inverter. Other inputs of the switch set are connected to the dividing counters, and the outputs thereof are connected through the reversible counter to the phase cycle integer reversible counter. The count pulse generator is connected to the first dividing counter, and the binary phase quantizer is connected to second inputs of the input shapers.
The above-mentioned digital tracking phase meter permits following the phase difference of input signals in any range of values and ensure optimal tracking of alterations of the input phase difference and the phase meter indication, whereby said phase meter can be used in phase-comparison radio-navigation systems. However, the foregoing phase meter is disadvantageous in that the interference immunity and speed of response thereof are not equally high throughout the measuring range. This irregularity in the phase difference measuring dynamic characteristics is attributed to nonlinearity of the digital tracking system upon which the tracking phase meter is based.
Still another digital tracking phase meter known in the art (cf. USSR Inventor's Certificate No. 576547, dated Nov. 15, 1977) comprises a shaper of narrow pulses corresponding to the forward edge of rectangular electric signals supplied to inputs of the digital tracking phase meter, one of said inputs being the input of said shaper, whose output is electrically connected to the input of the first switch whose output is connected to the input of the pulse counter whose counting input is electrically connected to a count pulse generator and the output thereof is connected to the input of control pulse distributor whose output is electrically connected to the countdown input of a reversible phase cycle integer counter whose countup input is electrically connected to an output of the switch of the control pulse distributor whose first input is electrically connected to the second input of the digital tracking phase meter, whereas respective outputs of the reversible phase cycle integer counter are connected to the countup and countdown inputs of the reversible phase cycle integer counter.
In said phase meter the count pulse generator is electrically connected to the countup input of the pulse counter via the first switch.
The control pulse distributor comprises apart from the switch a switching device, a code value comparator, a delay line and a flip-flop. The output of the switch is electrically connected to the countup and countdown inputs of the phase cycle fraction reversible counter via the code value comparator and the switching device coupled in series and is also electrically connected to the input of the flip-flop via the delay line. The output of the flip-flop is connected to the input of the switch whose another input is electrically connected to the input of the phase meter, whereas the input of the flip-flop is connected to the output of the narrow pulse shaper.
Electrical connection of the output of the pulse counter with the input of the control pulse distributor is effected through coupling the output of said pulse counter to the inputs of the code value comparator and the switching device, whose other inputs are connected to the output of the reversible phase cycle integer counter.
The linear tracking system upon which said phase meter is based provides for even interference immunity and speed of response throughout the measuring range. Yet, the construction of said phase meter is complicated, the aggregate is massive and the equipment includes such intricate devices as the code value comparator and switch set.